1. Technical Field
The present disclosure relates to an exposure device that detects a mask alignment mark (mask mark) formed on a mask and a workpiece alignment mark (workpiece mark) formed on a substrate (workpiece), performs alignment so that both marks are in a given positional relationship, and then exposes the workpiece through the mask. More particularly, the present disclosure relates to an exposure device capable of reducing the total time of an exposure process including alignment and exposure.
2. Related Art
In a process of forming a pattern of a semiconductor element, a printed board, and a liquid crystal substrate by photolithography, an exposure device is used. The exposure device aligns a mask having a mask pattern formed thereon and a substrate (hereinafter, also referred to as a workpiece), to which the pattern is transferred, in a given positional relationship, and then the workpiece is irradiated with light, including exposure light, through the mask. Accordingly, the mask pattern is transferred (exposure) to the workpiece.
FIG. 8 and FIG. 9 show that the exposure device divides the workpiece (printed board) into a plurality of exposure areas, and sequentially performs exposure for each of the divided areas while moving the workpiece.
As shown in FIG. 10, the workpiece is divided into four exposure areas A, B, C, and D, and alignment is performed for one exposure area using four workpiece marks (a, b, c, and d for the area A; and b, d, g, and h for the area B).
The mask and the workpiece have to be aligned in two plan directions (X direction and Y direction) and in a rotation direction (θ direction). For this reason, both the mask mark (mask alignment mark) and the workpiece mark (workpiece alignment mark) need to be provided as at least two parts. However, particularly when the workpiece is a printed board, the workpiece may expand and contract lengthwise and breadthwise due to the former process, and recently, four alignment marks are often used to improve alignment precision. In this case, the alignment is performed, for example, so that the sum of deviation in the coordinates of the mask marks and the workpiece marks becomes minimized.
As shown in FIG. 8 and FIG. 9, the exposure device mainly includes a light irradiation unit 1, a mask M, a mask stage MS for holding the mask, a projection lens 2, an exposure stage WS for performing an exposure process on a workpiece W (see FIG. 9) mounted thereon while sequentially moving, an alignment microscope 10 for detecting the mask marks and the workpiece marks, and a control unit 11 for controlling the whole operation of the exposure device.
The light irradiation unit 1 includes a lamp (not shown) for emitting exposure light.
A mask pattern MP that is transferred to the workpiece and mask marks MAM used for alignment to the workpiece are formed on the mask M. The mask stage MS is a stage for holding the mask M.
The projection lens 2 is a lens for projecting the mask pattern MP on the workpiece W.
The exposure stage WS is a stage for holding the workpiece W for an exposure process, and has a vacuum absorption groove (not shown) formed on a surface thereof. In addition, the exposure stage WS is provided with a reflection member MM (mirror) used for detecting a position of the mask mark MAM.
The exposure stage WS is provided with an XYθ moving mechanism (not shown) to align the mask M and the workpiece by moving the workpiece W. The XYθ moving mechanism has a stroke capable of moving the workpiece to each of the divided areas during exposure to move the workpiece in the X direction and the Y direction by a width of the workpiece.
The alignment microscope 10 is a microscope for detecting the mask marks MAM and the workpiece marks, and is provided according to the number of alignment masks (four in this case) detected in one exposure, and only two alignment microscopes are shown in FIG. 8 and FIG. 9. Images of the mask marks MAM or the workpiece marks detected by the alignment microscope 10 are processed in the control unit 11, and positional coordinates thereof are calculated. The alignment microscope 10 is configured to be inserted and withdrawn between the projection lens 2 and the exposure stage WS by an alignment microscope moving mechanism (not shown).
The alignment microscope 10 includes a half mirror 10a, lenses L1 and L2, and a CCD camera 10b. The control unit 11 is provided with a monitor 12 for displaying an image and the like received by the alignment microscope 10.
Next, an exposure sequence will be now described with reference to FIG. 8 and FIG. 9.
(1) As shown in FIG. 8, the mask M is irradiated with exposure light from the light irradiation unit 1, with no workpiece placed on the exposure stage WS.
The mask marks MAM formed on the mask are projected onto the reflection mirror MM of the exposure stage. The reflection mirror MM is provided at a position where the mask mark MAM is projected.
(2) The alignment microscope 10 is inserted between the projection lens 2 and the exposure stage WS. The projection image of the mask mark MAM reflected by the reflection mirror MM is reflected by the half mirror 10a of the alignment microscope 10 and is input to the CCD camera 10b. 
The image of the mask mark MAM input to the CCD camera 10b is transmitted to the control unit 11 and is processed, and positional coordinates thereof are calculated and stored.
(3) As shown in FIG. 9, the workpiece W subjected to an exposure process is transported to the exposure stage WS by a transporting mechanism (not shown) and is placed thereon.
(4) The alignment microscope 10 is inserted between the projection lens 2 and the exposure stage WS, and the workpiece marks WAM are detected. Alignment is performed by moving the exposure stage WS so that the detected workpiece marks WAM and the mask marks MAM stored in the process (2) are in a given relationship.
(5) After the alignment is completed, the alignment microscope 10 is withdrawn and exposure light is irradiated from the light irradiation unit 1. The mask pattern MP is projected and transferred onto the workpiece W by the projection lens 2.
(6) After the exposure is completed, the exposure stage WS is moved in the X direction or the Y direction, and then the next exposure area comes under the projection lens 2.
The processes (4) and (5) are repeatedly performed. That is, the alignment microscope 10 is inserted, the workpiece marks WAM are detected, and the alignment is performed, thereby performing the exposure.
In the same manner, the processes (4) to (6) are repeatedly performed. When all the divided areas on the workpiece are exposed, the exposure process of the workpiece is completed. The workpiece is taken out of the exposure device.
Recently, printed boards that are workpieces have become large, and the number of the exposure areas of the workpiece W is increased from the 4 divisions to 16 divisions as shown in FIG. 4. When the number of the divided exposure areas is increased, the exposure processing time for one workpiece is prolonged since the alignment and the exposure are performed in a serial sequence in the exposure method in which the detection and the alignment of the workpiece marks are performed in the exposure stage as described above.
To solve the problem, JP-A-2005-86093 describes the exposure device that includes a first stage for performing an exposure process, and a second stage for performing alignment measurement which is operable independently from the first stage. While the exposure process of the workpiece is performed in the first stage, the positional information of the workpiece on which the next exposure process will be performed is acquired (i.e., detection of workpiece marks) in the second stage.
With such a configuration, the alignment of the next workpiece is performed during the exposure process of another workpiece, and thus it is possible to shorten the time from the start of the exposure process of one workpiece to the end.
When classifying the related-art exposure device shown in FIG. 8 and FIG. 9 into an exposure processing unit including a first stage (hereinafter, referred to as an exposure stage) for performing an exposure process and an alignment stage unit including a second stage (hereinafter, referred to as an alignment stage) for performing alignment measurement, that is, detecting workpiece marks, in the same manner as an exposure device described in JP-A-2005-86093, the alignment stage unit is provided with an alignment stage, a stage moving mechanism for moving the stage in two directions (X and Y directions) perpendicular to each other by a width of the workpiece, and four alignment microscopes.
That is, as shown in FIG. 4, assuming that sixteen exposure areas formed by dividing the workpiece are A, B, C, D, . . . , N, O, and P, while the alignment stage repeats the sequential movement from the exposure area A in the X and Y directions, the alignment marks corresponding to the areas are detected by the alignment microscopes.
As described above, the exposure stage has to be moved in the X and Y directions by the width of the workpiece to expose each of the divided exposure areas. In addition, when the alignment stage is also moved in the X and Y directions by the width of the workpiece, it is necessary to secure a space where the exposure processing unit and the alignment stage unit can be moved in the X and Y directions by the width of the large workpiece. Accordingly, the size of the device becomes significantly large.
When the alignment stage is not moved to prevent this problem, 25 alignment microscopes, corresponding to all the workpiece marks shown in FIG. 4, are necessary. The alignment microscope is a precise optical device and is expensive, and thus the cost of the device being used is increased by using the 25 alignment microscopes.